A helium star is a class O or B star (blue), which has extraordinarily strong helium lines and weaker than normal hydrogen lines, indicating strong stellar winds and a mass loss of the outer envelope.
Therefore, pure helium stars have a maximum temperature, between about 100,000 K and 150,000 K depending on metallicity, because high luminosity causes dramatic inflation of the stellar envelope.
[3] Helium stars' great capability of transforming into other stellar objects has been observed over recent years since they were first identified.
The blue progenitor system of the supernova type Iax SN 2012Z in the spiral galaxy NGC 1309 is similar to the progenitor of the Galactic helium nova V445 Puppis, suggesting that SN 2012Z was the explosion of a white dwarf accreting from a helium-star companion.
It is observed to have caused a growing helium star that has the potential to transform into a red giant after losing its hydrogen envelope in the future.